GB2242025A

GB2242025A - Pressure sensor

Info

Publication number: GB2242025A
Application number: GB9103457A
Authority: GB
Inventors: Harry Kaiser; Andreas Reppich; Rainer Willig
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-03-15
Filing date: 1991-02-19
Publication date: 1991-09-18
Anticipated expiration: 2011-02-19
Also published as: DE4008320A1; ITMI910632A1; ITMI910632A0; GB2242025B; GB9103457D0; IT1245185B; JPH04221728A

Abstract

In a pressure sensor (11), the bottom part (13) consists of a baseplate rim (18) and a body (17), which are connected to one another with the aid of an elastic web (19) or web portions. If the bottom part (13) is mounted on a component, thanks to the elastic web (19) no mechanical stresses generating an undefined prestressing of a diaphragm (26) formed in the body (17) or of strain gauges thereon are produced during the mounting. As a result, measurement errors based on mechanical distortion due to the installation can be avoided. <IMAGE>

Description

11 - 1 Pressure sensor

Prior art

The invention is based on a pressure sensor of the generic type of Claim 1. In a known pressure sensor. the thick film substrate exhibiting the pressure diaphragm is supported in the bottom plate of the pressure sensor with the aid of a seal. There is some play between the thick film substrate and the bottom plate in. order to prevent any influence of mechanical distortion on the diaphragm. If, however, the bottom plate is screwed or riveted onto an uneven flange face, the bottom plate twists in such a manner that the thick film substrate is no longer supported by the desired annular area but, In the extreme case..- only on two points when pressure is applied to the pressure sensor. As a result, the thick film substrate bends over the entire cross-section, that is to say also in the area of the diaphragm. These mechanical distortions also act on the strain gauges applied to the diaphragm so that an undefined stress condition exists. These mechanical distortions thus falsify the measurement signal.

Advantages of the invention By comparison, the pressure sensor according to the invention, having the characterizing features of Claim 1. has the advantage that during the mounting of the bottom plate. onto a component, no mechanical distortions arise and thus no undefined stresses can be produced on the diaphragm. Measurement errors can thus be prevented. The number of parts is reduced which simplifies the mounting. During the mounting, no attention has to be paid to distortions being produced on the diaphragm of the thick film substrate by too great a tightening torque of the screws. Due to the asymmetric construction of the pressure sleeve, the latter can never be wrongly installed.

The measures listed in the subclaims provide for advantageous further developments of the pressure sensor specified in Claim 1.

Drawing Illustrative embodiments of the invention are shown in the drawing and explained in greater detail in the description following. Figure 1 shows a top view of the pressure sensor with a partially cut-open cover. Figure 2 shows a longitudinal section in direction II-II according to Figure 1, Figure 3 shows a perspective view of a detail and Figures 4, 4a and 5 each show a modification of the illustrative embodiment.

Description of the illustrative embodiments

In Figure 1, 10 designates the connector housing of a pressure sensor 11 which exhibits a central, stepped, continuous hole 12. Into this hole 12, a one-part bottom part of thick film substrate, for example steel granulate is inserted, in which arrangement an annular edge 14 of the connector housing 10 protrudes into an annular groove 15 formed in the bottom part 13. The edge 14 is fixed in the annular groove 15 with the aid of an adhesive 16. The bottom plate 13 is formed of one part but is divided by the annular groove 15 into a body 17 and into a baseplate 18 surrounding the body 17. In this arrangement, the annular groove 15 is constructed to be so deep that only a relatively thin web 19 exists which elastically but mechanically strongly connects the baseplate 18 and the body 17. The bottom part 13 also rests with the baseplate 18 against the underside of the connector housing 10. In the two narrower sides of the baseplate 18, four mounting holes 20 are in each case f ormed in order to attach the bottom part 13 to a component, not shown, with the aid of a screwed or riveted connection.

The body 17 of the bottom part 13 exhibits an approximately central recess 25 so that a thin area is produced which serves as diaphragm 26. Into the recess 251 a pressure sleeve 27 is inserted which Is fixed In the recess 25 with the aid of a retaining washer 28. In the outside wall of the pressure sleeve 27. annular grooves 29 with seals 30 located therein are formed for the purpose of sealing.

The connector housing 10 exhibits laterally mounted electrical contacts 32. Furthermore, an annular groove 33 is formed at the top of the connector housing 10 in which an edge 34 of a cover 35 is attached. The cover 35 exhibits a venting hole 36 which is closed by pressing-in a ball 37 after the cover 35 has been bonded.

In the area of the diaphragm 26. several strain gauges 40 are arranged in the form of a resistance measuring bridge. However. other resistors which change their electrical properties with deformation such as, for example, thick film or thin film resistors, can also be used. The conductor tracks 42 applied to the top of the body 17 are connected to the contacts 32 of the connector housing 10 with the aid of bonding wires 42. Furthermore, an electronic hybrid circuit 43 can also be printed onto the body 17. To protect them against environmental influences, the strain gauges 40, the conductor tracks 42 and the hybrid circuit 43 are covered by a sealing compound 44.

The function of a pressure sensor 11 is adequately known and does not therefore need to be described in' detail at this point. The pressure to be determined, which can have a magnitude of up to 200 bar,, is supplied to a diaphragm 26 with the aid of the pressure sleeve 27. The sealing rings 30 seal the recess 25 in this arrangement. Due to the action of the pressure, the diaphragm 26 is bent through so that the strain gauges 40 are also influenced in their electrical behaviour. The resultant electrical measurement signal can be supplied via the conductor tracks 42, the bonding wires 41 and the con- tacts 32 of the connector housing 10 to an evaluating circuit. not shown.

During the assembly of the pressure sensor 11. the projections 19 of the connector housing 10 are inserted into the annular groove 15 and attached with the aid of the adhesive 16. The bottom part 13 is subsequently screwedt for example, onto a component,, not shown. In this connection, care must be taken so that no mechanical distortions are produced which would slightly deform the diaphragm 26 already in a condition where no pressure is applied. As a result, prestresses could occur in an undefinable manner in the strain gauges 40 which would lead to measurement errors. To avoid or largely to reduce these measurement errors, the web 19 is constructed to be elastically movable. If the bottom part 13 is attached. that is to say screwed or riveted onto an uneven face of a component, the baseplate 18 can slightly bend and adapt to the surface shape in the area of the web 19 compared with the body 17 without mechanical stresses being created in the bottom part 13. The bottom part 13, and thus the pressure sensor 11, is attached to the coiponent with the aid of the mounting holes 20. Due to the elastic construction of the web 19. no mechanical distortions can occur in the area of the diaphragm 26 as a result of the mounting.

In the illustrative embodiment according to Figure 3, the web 19 is produced in such a manner that an annular groove 15 is created in the bottom part 13 from one side. As can be seen from Figure 4, however, the body 17 can also be suspended in the baseplate 18 with the aid of carriers 48. In this arrangement, it is possible that there are three carriers 48 which are arranged with a spacing of 120 degrees. If the number of carriers is an integral multiple of 3, the angular spacings are 60. 30 and so forth degrees. However, the body 17 can also be attached in the baseplate 18 by means of four carriers 48a, the spacing between the carriers 48a then being 90 degrees. Here, too, the body 17 can be suspended in the baseplate 18 with a multiple of four carriers 48a and 1 is with the corresponding multiple of 90 degrees, respectively.

In the illustrative embodiment according to Figure 5,, the connector housing 10 is not bonded into the bottom part 13. Instead, an annular recess 50 Is formed in the bottom part 13 in the outside wall of the annular groove 15. that is to say In the wall facing away from the body 17, into which recess a sealing ring 51 is inserted. The projections 14 of the connector housing 10 are thus inserted into the annular groove 15 during the mounting and. due to the prestressing of the sealing ring 50. the connector housing 10 in fixed in the bottom part 13 and at the same time also sealed by the scaling ring. The remaining mode of operation and the modifications shown in Figures 4 and 4a are also applicable In this case.

Claims

1. Pressure sensor (11) comprising a connector housing (10) exhibiting electrical contacts (32) and a pressure-dependently deformable diaphragm (26) constructed in a housing part (13). the deformation of which is detected with the aid of electrical resistors (40) which change their electrical properties with deformation, the housing part (13) being connected in a form-locking manner to the connector housing (10) and directly or indirectly to a component, characterised in that the housing part (13) consists of a part (17) exhibiting the diaphragm (26) and an edge (18) for attaching mounting means and in that the part (17) and the edge (18) are elastically and movably connected to one another.

2. Pressure sensor according to Claim 1, characterised in that the housing part (13) is constructed of one part and in that a relatively thin elastically deformable area (19) is located between the part (17) and the edge (18).

3. Pressure sensor according to Claim 1, characterised in that the housing part (13) is constructed of one part and in that the part (17) and the edge (18) are elastically connected to one another with the aid of at least three carriers (48).

4. Pressure sensor according to Claim 3, characterised in that the carriers (48) are arranged with a spacing of a multiple of 120 degrees.

5. Pressure sensor according to Claim 3,, characterised in that the carriers (48) are arranged with a spacing of a multiple of 90 degrees.

6. Pressure sensor according to Claim 2,, characterised in that an annular groove (15) is constructed in the top of the housing part (13) so that a web (19) is 1 produced between the part (17) and the edge (18).

7. Pressure sensor according to one of Claims 1 to 6, characterised in that projections (14) protrude into the annular groove (15) at the connector housing (10).

8. 1 Pressure sensor according to Claim 7.. characterised in that the projections (14) are bonded into the annular groove (15).

9. Pressure sensor according to one of Claims 1 to 8. characterised in that the housing part (13) consists of thick film substrate.

10. Pressure sensor according to one of Claims 1 to 9, characterised in that the resistors (40) are connected to the electrical contacts (32) of the connector housing (10) with the aid of bonding wires (41).

11. Any of the pressure sensors substantially as herein described with reference to the accompanying drawings.

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